Add comment for public_member_api_docs

Author: peixinli

packages/google_sign_in/google_sign_in_web/lib/src/js_interop/gapi.dart

@@ -11,6 +11,8 @@
 // https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/gapi
 
 // ignore_for_file: public_member_api_docs,
+// * public_member_api_docs originally undocumented because the file was
+//   autogenerated.
 
 @JS()
 library gapi;

packages/google_sign_in/google_sign_in_web/lib/src/js_interop/gapiauth2.dart

@@ -13,6 +13,8 @@
 // https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/gapi.auth2
 
 // ignore_for_file: public_member_api_docs, non_constant_identifier_names,
+// * public_member_api_docs originally undocumented because the file was
+//   autogenerated.
 // * non_constant_identifier_names required to be able to use the same parameter
 //   names as the underlying library.